Methods of coating an electrically conductive substrate and related electrodepositable compositions

ABSTRACT

A method of producing an electrode for a lithium ion battery is disclosed in which an electrically conductive substrate is immersed into an electrodepositable composition, the substrate serving as the electrode in an electrical circuit comprising the electrode and a counter-electrode immersed in the composition, a coating being applied onto or over at least a portion of the substrate as electric current is passed between the electrodes. The electrodepositable composition comprises: (a) an aqueous medium; (b) an ionic (meth)acrylic polymer; and (c) solid particles comprising: (i) lithium-containing particles, and (ii) electrically conductive particles, wherein the composition has a weight ratio of solid particles to ionic (meth)acrylic polymer of at least 4:1.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser.No. 13/686,003, filed Nov. 27, 2012.

FIELD

The present invention relates to methods of producing a lithium ionbattery by electrodeposition. The present invention is also related toelectrodepositable compositions for producing a lithium ion-containingbattery.

BACKGROUND

Electrodeposition as a coating application method involves thedeposition onto an electrically conductive substrate of a compositionunder the influence of an applied electrical potential. A coating isdeposited as the substrate is immersed in the composition, the substrateserving as an electrode in an electrical circuit of the electrode and acounter-electrode immersed in the composition, the coating being appliedto the substrate as electric current is passed between the electrodes.

Often, the composition used in an electrodeposition process includes aresinous phase dispersed in an aqueous medium. While the compositioninto which the substrate is immersed may include pigments to providecolor and other fillers and additives, the properties historicallysought by electrodeposited coatings, such as outstanding corrosionresistance, arise primarily because of the deposition of a continuousresinous film. Therefore, the resin content of the composition intowhich the substrate is immersed is relatively high in relation to theamount of pigment and other fillers. For example, such compositionsusually contain 0.02 to 1 parts by weight pigment to 1 part by weightresinous phase.

Lithium ion batteries consist of a cathode, an anode, a separator, andan electrolyte. The cathode is a metal (often aluminum) foil substratehaving a lithium-containing active material, such as LiFePO₄, depositedthereon. The lithium-containing active material is deposited on thesubstrate from a slurry containing the lithium-containing activematerial, conductive carbon, and binder (such as polyvinylidenedifluoride) in organic solvent (such as n-methyl-2-pyrrolidone) via aslot die coater. In these slurries, the sum of the amount oflithium-containing active material and conductive carbon is highrelative to the amount of binder, typically at least 9 parts by weightto 1 part by weight. The use of such solvent-borne slurries is, however,environmentally undesirable.

As a result, alternative methods and compositions for depositinglithium-containing compositions on a metal foil are desired. The presentinvention was made in view of the foregoing.

SUMMARY OF THE INVENTION

The present invention is directed to a method of producing an electrodefor a lithium ion battery. The method comprises immersing anelectrically conductive substrate into an electrodepositablecomposition, the substrate serving as the electrode in an electricalcircuit comprising the electrode and a counter-electrode immersed in thecomposition, a coating being applied onto or over at least a portion ofthe substrate as electric current is passed between the electrodes. Theelectrodepositable composition used in this method comprises: (a) anaqueous medium; (b) an ionic (meth)acrylic polymer, and (c) solidparticles comprising: (i) lithium-containing particles, and (ii)electrically conductive particles and has a weight ratio of solidparticles to ionic (meth)acrylic polymer of at least 4:1.

The present invention is also directed to electrodepositablecompositions comprising: (a) an aqueous medium; (b) an ionic(meth)acrylic polymer; and (c) solid particles comprising: (i)lithium-containing particles, and (ii) electrically conductiveparticles, wherein the composition has a weight ratio of solid particlesto ionic (meth)acrylic polymer of at least 4:1.

DETAILED DESCRIPTION

For purposes of the following detailed description, it is to beunderstood that the invention may assume various alternative variationsand step sequences, except where expressly specified to the contrary.Moreover, other than in any operating examples, or where otherwiseindicated, all numbers expressing, for example, quantities ofingredients used in the specification and claims are to be understood asbeing modified in all instances by the term “about”, Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances.

As used herein, the term “polymer” refers to copolymers and oligomers.

The term “(meth)acrylic” refers to both acrylic and methacrylic monomersand polymers.

In certain embodiments, the substrate is embodied in the form of asheet, coil, or foil. As used herein, the term “foil” refers to a thinand pliable sheet of metal. Such foils may be constructed of forexample, aluminum, iron, copper, manganese, nickel, combinationsthereof, and/or alloys thereof. In certain embodiments, the thickness ofthe foil, such as a foil comprising aluminum, is no more than 8 mils(203.2 μm), such as no more than 4 mils (101.6 μm), no more than 2 mils(50.8 μm), or, in some cases no more than 1 mil (25.4 μm), and/or atleast 0.1 mil (2.54 μm), such as at least 0.2 mil (5.08 μm), at least0.4 mils (10.2 μm), or at least 0.5 mil (12.7 μm).

The methods of the present invention comprise immersing the electricallyconductive substrate into an electrodepositable composition, thesubstrate serving as an electrode for a lithium ion battery in anelectrical circuit comprising the electrode and a counter-electrodeimmersed in the composition, a coating being applied onto or over atleast a portion of the substrate as electric current is passed betweenthe electrodes.

As used herein, the term “electrodepositable composition” refers to acomposition that includes components that are electrodepositable. Asused herein, the term “electrodepositable” means capable of beingdeposited onto an electrically conductive substrate under the influenceof an applied electrical potential.

The electrodepositable compositions used in the methods of the presentinvention comprise an aqueous medium. As used herein, the term “aqueousmedium” refers to a medium that either consists exclusively of water orcomprises predominantly water in combination with inert organiccosolvent(s).

In certain embodiments, the aqueous medium is present in the compositionused in the methods of the present invention in an amount of at least 75percent by weight, at least 90 percent by weight, or at least 95 percentby weight, such as 75 to 99.5 percent by weight, 90 to 99 percent byweight, or, in some cases, 95 to 99 percent by weight, based on thetotal weight of the composition. In other words, the compositions usedin the methods of the present invention may have a relatively low totalsolids content, as described further below.

The electrodepositable compositions used in the methods of the presentinvention comprise an ionic (meth)acrylic polymer. As used herein, theterm “ionic” refers to a (meth)acrylic polymer that carries a charge,including (meth)acrylic polymers that carry a negatively charged ion and(meth)acrylic polymers that carry a positively charged ion. Suitableionic (meth)acrylic polymers include, therefore, anionic (meth)acrylicpolymers and cationic (meth)acrylic polymers.

Suitable anionic (meth)acrylic polymers contain at least partiallyneutralized anionic groups, such as acid groups, such as carboxylic acidgroups, which impart a negative charge. Non-limiting examples ofsuitable anionic (meth)acrylic polymers, therefore, includebase-neutralized, carboxylic acid group-containing polymers.

The ionic (meth)acrylic polymers are water dispersible. As used herein,a “water dispersible ionic (meth)acrylic polymer” means that the polymeris capable of being distributed throughout water as finely dividedparticles. See R. Lewis, Sr., Hawley's Condensed Chemical Dictionary,(12th Ed. 1993) at page 435.

Examples of (meth)acrylic polymers are those which are prepared bypolymerizing mixtures of (meth)acrylic monomers. The (meth)acrylicpolymer contains carboxylic acid moieties that are introduced into thepolymer from the use of (meth)acrylic carboxylic acids. The carboxylicacid functionality provides sites for subsequent neutralization with abase such as an organic amine to stabilize the polymer dispersed inaqueous medium. The unsaturated carboxylic acid will constitute from 20to 60, such as 30 to 50 percent by weight of the total weight ofmonomers used in preparing the (meth)acrylic polymer. Examples of(meth)acrylic carboxylic acids are acrylic acid and (meth)acrylic acid.

The (meth)acrylic polymer typically contains a “soft” polymer segmentfrom the use of a monomer having a glass transition temperature of −20°C. or less. Examples of such monomers are alkyl acrylates containingfrom 4 to 8 carbon atoms in the alkyl group such as butyl acrylate and2-ethylhexyl acrylate. Such monomers will constitute from 30 to 70, suchas 40 to 60 percent by weight of the total weight of the monomers usedin preparing the (meth)acrylic polymer.

Glass transition temperatures (Tg) of (meth)acrylic monomers are widelyreported in the literature. Examples of (meth)acrylic monomers and Tgslows:

Monomer Tg, ° C. Methacrylic acid 228 Acrylic acid 105 Hydroxyethylmethacrylate 57 Butyl methacrylate 20 2-Ethylhexyl acrylate −50 n-Butylacrylate −54

Examples of other (meth)acrylic monomers that can be used in preparingthe (meth)acrylic polymers are alkyl methacrylates containing from 4 to6 carbon atoms in the alkyl group such as butyl methacrylate and hexylmethacrylate and alkyl acrylates having 1 to 3 carbon atoms in the alkylgroup such as methyl acrylate and ethyl acrylate. These (meth)acrylicmonomers typically constitute up to 20 percent by weight based on totalweight of monomers used in preparing the (meth)acrylic polymer.

Vinyl monomers can optionally be used in preparing the (meth)acrylicpolymer. Examples of such monomers are vinyl aromatic monomers such asstyrene and alpha-methyl styrene. If used, these monomers constitute upto 10 percent by weight based on total weight of monomers used inpreparing the (meth)acrylic polymer.

The (meth)acrylic polymer typically has a glass transition temperatureof less than 20° C., such as less than 0° C. to provide the necessaryflexibility in the resultant electrodeposited coating. The term “glasstransition temperature” (Tg) is a theoretical value being the glasstransition temperature as calculated by the method of Fox on the basisof monomer composition of the monomer charges according to T. G. Fox,Bull. Am. Phys. Soc. (Se. II) 1, 123 (1056) and J. Brandrup, E. H.Immergut, Polymer Handbook 3^(rd) edition, John Wiley, New York, 1989.

The (meth)acrylic polymers will typically have molecular weights of atleast 2000, such as 4000 to 500,000 on a weight average basis (Mw) asdetermined by gel permeation chromatography using polystyrene standards.

The electrodepositable compositions are typically thermosetting innature by the presence of curing agent. The curing agents can beintegral with the (meth)acrylic polymer or they can be present as aseparate component.

Curing agents which are integral with the (meth)acrylic polymer areincorporated into the polymer by including within the monomer chargepolymerizable (meth)acrylic monomers containing self-curing groups.Examples of monomers which contain self-curing groups include N-methylolether derivatives of acrylic and methacrylic amides. When these monomersare employed, they constitute up to 30, such as up to 20 percent byweight of the monomers used in preparing the (meth)acrylic polymer. Suchself-curing groups are stable when the (meth)acrylic polymer-containingcompositions are at room temperature, that is, about 20°-25° C., butunder the influence of heat, are reactive with each other or with otheractive hydrogen groups in the polymer such as hydroxyl groups andcarboxylic acid groups to crosslink the polymer. Suitable N-methylolether derivatives of acrylic acid and methacrylic acid amides areN-butoxymethyl acrylamide and N-methoxymethyl methacrylamide.

Besides self-curing (meth)acrylic polymers, thermosetting compositionscan be formed from (meth)acrylic polymers containing active hydrogensand a curing agent which is present in the coating composition as aseparate component, for example, an aminoplast. The curing agent is onewhich is stable in the presence of the active hydrogen-containingacrylic polymer at room temperature, that is 20°-25° C., but is reactivewith the active hydrogens under the influence of heat to form a cured orcrosslinked product.

Active hydrogens are incorporated into the (meth)acrylic polymer byincluding with the monomer charge monomers containing hydroxyl groups.Examples of (meth)acrylic monomers containing hydroxyl groups arehydroxyalkyl acrylates and methacrylates. Preferably, the hydroxyalkylgroup will contain from 2 to 4 carbon atoms and examples would includehydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylateand hydroxypropyl methacrylate.

The (meth)acrylic monomers containing the active hydrogens (exclusive ofthe carboxylic acid containing monomer) can be used in amounts of up to30, usually up to 15 percent by weight, based on total weight of themonomers used in preparing the (meth)acrylic polymer.

As mentioned above, the externally added curing agent is one which isstable with the (meth)acrylic polymer at room temperature (20°-25° C.)but reactive with the active hydrogens of the (meth)acrylic polymer atelevated temperature, that is, 135-200° C., to form a cured orcrosslinked product. Preferred curing agents are water-soluble orwater-dispersible aminoplasts. The aminoplasts are aldehyde condensationproducts of melamine, benzoguanamine, urea or similar compounds.Generally, the aldehyde employed is formaldehyde, although usefulproducts can be made from other aldehydes such as acetaldehyde,crotonaldehyde, acrolein, benzaldehyde, furfural and others.Condensation products of melamine, urea or benzoguanamine are mostcommon and are preferred but products of other amines and amides inwhich at least one amino group is present can also be employed. Forexample, such condensation products can be produced from variousdiazines, triazoles, guanidines, guanamines and alkyl and di-substitutedderivatives of such compounds including alkyl and aryl-substituted ureasand alkyl and aryl-substituted melamines and benzoguanamines. Examplesof such compounds are N,N-dimethyl urea, N-phenyl urea, dicyandiamide,formoguanamine, acetoguanamine, 6-methyl-2,4-diamino-1,3,5-triazine,3,5-diaminotriazole, triaminopyrimidine,2,4,6-triethyltriamine-1,3,5-triazine and the like.

These amine-aldehyde condensation products contain methylol groups orsimilar alkylol groups depending upon the particular aldehyde employed.If desired, these methylol groups can be etherified by reaction with analcohol. Various alcohols are employed for this purpose includingessentially any monohydric alcohol, although the preferred alcoholscontain from 1 to 4 carbon atoms such as methanol, ethanol, isopropanoland n-butanol.

The (meth)acrylic polymer can be prepared by free radical initiatedsolution polymerization techniques in which the polymerizable monomersare dissolved in organic solvent and polymerized in the presence of afree radical initiator such as azobisisobutyronitrile or benzoylperoxide. Alternatively, the (meth)acrylic polymer can be prepared inaqueous medium by emulsion polymerization techniques.

To prepare the (meth)acrylic polymer by solution polymerizationtechniques, the solvent is first heated to reflux and the mixture ofpolymerizable monomers containing the free radical initiator is addedslowly to the refluxing solvent. The reaction mixture is held atpolymerizing temperatures so as to reduce the free monomer content tobelow 1.0 and usually below 0.5 percent.

The (meth)acrylic polymer prepared as described above typically has amolecular weight on a weight average basis of about 2000 to 50,000, suchas 4000 to 25,000.

The acid group-containing (meth)acrylic polymer is treated with a baseto form a water-dispersible salt thereof. Examples of suitable bases areinorganic bases such as sodium and potassium hydroxides. Preferably thebase is an amine. Examples of suitable amines are water-soluble aminesincluding ammonia, primary, secondary and tertiary amines includinghydroxyalkyl amines. Examples include ethanolamine, diethanolamine,N-methylethanolamine, ethylamine and diethylamine. The acidgroup-containing polymer is at least partially neutralized, usually tothe extent of at least 20 and more usually at least 40 percent of thetotal theoretical neutralization.

After the acid group-containing (meth)acrylic polymer has been treatedwith a base, it is dispersed in aqueous medium. The step of dispersionis accomplished by combining the neutralized or partially neutralizedpolymer with the aqueous medium. Neutralization and dispersion can beaccomplished in one step by combining the acid group-containing acrylicpolymer and aqueous medium which contains the base. The polymer (or itssalt) can be added to the aqueous medium or the aqueous medium added tothe polymer (or its salt). The pH of the dispersion is preferably withinthe range of 7.0 to 9.0.

The (meth)acrylic polymers can also be prepared by emulsionpolymerization techniques well known in the art. Examples of suitabletechniques involve the pre-emulsification technique and the seedingtechnique. In the pre-emulsification technique, a small amount of wateris present in the polymerization vessel together with a polymerizationinitiator and optionally all or part of the emulsifying agent. Themonomer charge is emulsified in a larger amount of water and iscontinuously added to the reaction vessel under polymerizing conditions.If all the emulsifier is not present initially in the reaction vessel,it can be added simultaneously with the monomer addition. Alternately,the total amount of water may be present in the reaction vessel and themonomers added in bulk form.

In the seeding technique, a small amount of the monomer charge is addedto the reaction vessel along with all or part of the polymerizationinitiator and all or part of the emulsifier and polymerized to form aseed latex. After formation of the seed latex, the remainingpolymerization ingredients are added in a continuous manner to thereaction vessel under polymerizing conditions to form the final polymeremulsion.

The (meth)acrylic polymers prepared as described above typically havemolecular weights on a weight average basis of about 25,000 to 500,000,such as 50,000 to 100,000 as determined by gel permeation chromatographyusing polystyrene standards.

To form the ionic salt of the (meth)acrylic monomer, the latices arerendered alkaline in pH in the range of 7.5 to 9.5 by adding ammonia ora water-soluble amine to the latex.

In other embodiments of the present invention, the ionic resin comprisesa cationic salt group-containing resin. Suitable cationic salt-groupcontaining resins include resins that contain at least partiallyneutralized cationic groups, such as sulfonium groups and amine groups,which impart a positive charge.

The cationic resin may comprise a water soluble cationic resin. Incertain embodiments, the water soluble cationic resin comprises apoly(C₂₋₄)-alkyleneimine, which can be linear or branched, specificexamples of which include polyethyleneimines (PEIs). As will beappreciated, PEIs are made by a ring opening polymerization ofethylenamine. Other suitable water soluble cationic resins includepoly(allylamine hydrochloride),poly(acrylamide-co-diallyldimethylammonium chloride) andpoly(2-methacryloxyethyltrimethylammonium chloride). In certainembodiments, the water soluble cationic resin, such as those mentionedabove, has a weight average molecular weight of at least 5,000, such asat least 10,000, or, in some cases, 5,000 to 50,000, or, in some cases10,000 to 25,000 as determined by gel permeation techniques usingpolystyrene standards.

Typically, the water soluble cationic resin, such as a PEI, is presentin an amount of at least 50 percent by weight, such as at least 60percent by weight, at least 70 percent by weight, at least 80 percent byweight, or, in some cases, at least 90 percent by weight, based on thetotal weight of resin in the composition. In certain embodiments, thewater soluble cationic resin, such as a PEI, is present in an amount ofno more than 20 percent by weight, no more than 15 percent by weight, nomore than 10 percent by weight, no more than 5 percent by weight, suchas 1 to 20 percent by weight, 1 to 15 percent by weight, 5 to 15 percentby weight, or, in some cases, 1 to 3 percent by weight, based on thetotal weight of solids in the composition.

The composition may comprise a water dispersible cationic resin.Examples of water dispersible cationic resins that are suitable for usein the compositions described herein are active hydrogen-containing,cationic salt group-containing resins. As used herein, the term “activehydrogen-containing, cationic salt group-containing resin” refers toresins that include active hydrogen functional groups and at leastpartially neutralized cationic groups. Examples of resins that aresuitable for use as the active hydrogen-containing, cationic saltgroup-containing resin in the present invention include, but are notlimited to, alkyd resins, acrylics, polyepoxides, polyamides,polyurethanes, polyureas, polyethers, and polyesters, among others.

More specific examples of suitable active hydrogen-containing, cationicsalt group containing resins include polyepoxide-amine adducts, such asthe adduct of a polyglycidyl ethers of a polyphenol, such as bisphenolA, and primary and/or secondary amines, such as are described in U.S.Pat. No. 4,031,050 at col. 3, line 27 to col. 5, line 50, U.S. Pat. No.4,452,963 at col. 5, line 58 to col. 6, line 66, and U.S. Pat. No.6,017,432 at col. 2, line 66 to col. 6, line 26, these portions of whichbeing incorporated herein by reference. In certain embodiments, aportion of the amine that is reacted with the polyepoxide is a ketamineof a polyamine, as is described in U.S. Pat. No. 4,104,147 at cot. 6,line 23 to col. 7, line 23, the cited portion of which beingincorporated herein by reference. Also suitable are ungelledpolyepoxide-polyoxyalkylenepolyamine resins, such as are described inU.S. Pat. No. 4,432,850 at col. 2, line 60 to col. 5, line 58, the citedportion of which being incorporated herein by reference. In addition,cationic acrylic resins, such as those described in U.S. Pat. No.3,455,806 at col. 2, line 18 to col. 3, line 61 and U.S. Pat. No.3,928,157 at col. 2, line 29 to col. 3, line 21, these portions of bothof which being incorporated herein by reference, can be used.

Besides amine salt group-containing resins, quaternary ammonium saltgroup-containing resins can also be employed as a cationic saltgroup-containing resin in the compositions described herein. Examples ofthese resins are those which are formed from reacting an organicpolyepoxide with a tertiary amine acid salt. Such resins are describedin U.S. Pat. No. 3,962,165 at col. 2, line 3 to col. 11, line 7, U.S.Pat. No. 3,975,346 at col. 1, line 62 to col. 17, line 25, and U.S. Pat.No. 4,001,156 at col. 1, line 37 to col. 16, line 7, these portions ofwhich being incorporated herein by reference. Examples of other suitablecationic resins include ternary sulfonium salt group-containing resins,such as those described in U.S. Pat. No. 3,793,278 at col. 1, line 32 tocol. 5, line 20, this portion of which being incorporated herein byreference. Also, cationic resins which cure via a transesterificationmechanism, such as described in European Patent Application No. 12463B1at p. 2, line 1 to p. 6, line 25, this portion of which beingincorporated herein by reference, can also be employed.

Other suitable cationic salt group-containing resins include those thatmay form photodegradation resistant electrodepositable coatingcompositions. Such resins include the resins comprising cationic aminesalt groups which are derived from pendant and/or terminal amino groupsthat are disclosed in United States Patent Application Publication2003/0054193 A1 at [0064] to [0088], this portion of which beingincorporated herein by reference. Also suitable are the activehydrogen-containing, cationic salt group-containing resins derived froma polyglycidyl ether of a polyhydric phenol that is essentially free ofaliphatic carbon atoms to which are bonded more than one aromatic group,which are described in United States Patent Application Publication US2003/0054193 A1 at [0096] to [0123], this portion of which beingincorporated herein by reference.

The compositions comprising a cationic resin composition may comprise awater soluble cationic resin, such as a PEI, and a water dispersiblecationic resin, different from the PEI, wherein the water dispersiblecationic resin is present in the composition in an amount of less than50 percent by weight, such as less than 40 percent by weight, less than30 percent by weight, less than 20 percent by weight, or, in some cases,less than 10 percent by weight, based on the total weight of cationicresin in the composition.

As will be appreciated, in adapting the cationic resin to be solubilizedor dispersed in an aqueous medium, the resin is at least partiallyneutralized by, for example, treating with an acid. Non-limitingexamples of suitable acids are inorganic acids, such as phosphoric acidand sulfamic acid, as well as organic acids, such as, acetic acid andlactic acid, among others. Besides acids, salts such asdimethylhydroxyethylammonium dihydrogenphosphate and ammoniumdihydrogenphosphate can be used. In certain embodiments, the cationicresin is neutralized to the extent of at least 50 percent or, in somecases, at least 70 percent, of the total theoretical neutralizationequivalent. The step of solubilization or dispersion may be accomplishedby combining the neutralized or partially neutralized resin with thewater.

The composition further includes a curing agent to react with the activehydrogen groups of the cationic salt group containing resin describedabove. Non-limiting examples of suitable curing agents arepolyisocyanates, including at least partially blocked polyisocyanates,aminoplast resins and phenolic resins, such as phenolformaldehydecondensates including allyl ether derivatives thereof.

The electrodepositable compositions comprise lithium-containingparticles, such as, for example, LiCoO₂, LiNiO₂, LiFePO₄, LiCoPO₄,LiMnO₂, LiMn₂O₄, Li(NiMnCo)O₂, and/or Li(NiCoAl)O₂. Thelithium-containing particles typically have an average particle size,prior to incorporation into the composition, of no more than 10 micron,no more than 5 micron, no more than 3 micron, no more than 1 micron,such as 10 nanometers to 1,000 nanometers, or, in some cases 500nanometers to 1,000 nanometers or 600 nanometers to 800 nanometers.

The lithium-containing solid particles are present in theelectrodepositable composition in an amount of at least 50 percent byweight, at least 60 percent by weight, at least 70 percent by weight, atleast 80 percent by weight, such as at least 85 percent by weight, or,in some cases, at least 90 percent by weight, based on the total weightof solids in the composition.

In addition to the lithium-containing particles, the electrodepositablecomposition comprises electrically conductive particles, such aselectrically conductive carbon particles. Suitable electricallyconductive particles include electrically conductive carbon blacks.Examples of commercially available electrically conductive carbonblacks, that are suitable for use herein, include, but are not limitedto, Cabot Monarch™ 1300, Cabot XC-72R, Black Pearls 2000 and Vulcan XC72 sold by Cabot Corporation; Acheson Electrodag™ 230 sold by AchesonColloids Co.; Columbian Raven™3500 sold by Columbian Carbon Co.; andPrintex™ XE 2, Printex 200, Printex L and Printex L6 sold by DeGussaCorporation, Pigments Group, and Super P® and Super P® Li, C-Nergy™Super C45 and C-Nergy™ Super C65 sold by TIMCAL Ltd.

The electrically conductive carbon particles typically have an averageparticle size, prior to incorporation into the composition, of less than300 nanometers, such as 1 to 200 nanometers, 10 to 100 nanometers, or,in some cases, 30 to 50 nanometers.

The electrically conductive carbon particles are typically present inthe composition in an amount such that the relative weight ratio oflithium-containing particles to electrically conductive particles in thecomposition is at least 3:1, at least 4:1, at least 5:1, at least 8:1,at least 10:1, or, in some cases, at least 15:1. The electricallyconductive carbon particles are present in an amount of no more than 20percent by weight, no more than 10 percent by weight, such as 1 to 10percent by weight, or 1 to 5 percent by weight, based on the totalweight of the solids in the composition.

The electrodepositable composition may include other typicalingredients, such as adjuvant polymers such as polyvinylidenedifluoride, corrosion inhibitors, anti-oxidants, flow control agents andsurfactants.

The compositions described above can be prepared in any desired manner,including the methods described in the Examples. For example, in someembodiments, it may be desirable to incorporate the solid particles bymeans of a composition in which the solid particles are mixed with ionic(meth)acrylic polymer that has been pro-solubilized in an aqueousmedium. The solids content of such a composition may be relatively high,such as 2 times, 3 times, or 4 times or more the total solids content ofthe composition in the methods of the present invention. The compositionmay be mixed, such as by sonication, to provide a uniform dispersion.This sonication may take 15 to 30 minutes or more. The resultingcomposition may then subsequently be combined with further liquidcarrier, i.e., water and optionally organic solvent, to provide thefinal composition for use in the methods of the present invention.

In the method of the present invention, the substrate is immersed in acomposition that has a weight ratio of solid particles(lithium-containing particles and carbon particles) to ionic polymer ofat least 4:1, such as at least 5:1, at least 6:1, at least 7:1, at least8:1, at least 9:1, at least 10:1, at least 11:1, at least 12:1, at least13:1, at least 14:1, at least 15:1, at least 16:1, at least 17:1, orhigher. Moreover, the substrate is immersed in a composition that has atotal solids content of 0.5 to 25 percent by weight, such as 1 to 10percent by weight, or, in some cases, 1 to 5 percent by weight, based onthe total weight of the composition. Indeed, it has been discovered thatsuch compositions can be provide stable dispersions of the solidparticles and ionic polymer in an aqueous medium, even without the useof a thickener. As used herein, the term “stable dispersion” refers to adispersion that does not gel, flocculate or precipitate when maintainedat a temperature of 25° C. for at least 60 days, or, if someprecipitation does occur, the precipitate can be radispersed uponagitation.

Moreover, it has been discovered that when such compositions are used inthe methods of the present invention, even when the weight ratio ofsolid particles (such as lithium-containing particles in combinationwith electrically conductive carbon particles) to ionic polymer in thebath is within the foregoing ranges, a solid uniform coating of asuitable film thickness and limited porosity can be provided, which maymake the foregoing methods particularly suitable for manufacturingcoated substrates that may be used as a cathode for a lithium ionbattery.

In the methods of the present invention, a coating is applied onto orover at least a portion of the substrate via an electrodepositionprocess. In such a process, an electrically conductive substrate (suchas any of those described earlier) serving as an anode in an electricalcircuit comprising the anode and cathode is immersed in a composition ofthe type described above. An electric current is passed between theelectrodes to cause the coating to deposit on the anode. The appliedvoltage may be varied and can be, for example, as low as one volt to ashigh as several thousand volts, but is often between 50 and 500 volts.The current density is often between 0.5 ampere and 15 amperes persquare foot. In certain embodiments, the residence time of the substratein the composition is from 30 to 180 seconds.

After electrocoating, the substrate is removed from the bath and may, incertain embodiments and depending upon the particulars of thecomposition and the preferences of the end user, be baked in an oven.For example, the coated substrate may be baked at temperatures of 200°C. or lower, such as 125-175° C.) for 10 to 60 minutes.

EXAMPLES

The following examples are offered to aid in understanding of thepresent invention and are not to be construed as limiting the scopethereof. Unless otherwise indicated, all parts and percentages are byweight.

Two (2) (meth)acrylic polymers were prepared as described in Examples 1and 2. The (meth)acrylic polymer of Example 1 was prepared by emulsionpolymerization techniques. The (meth)acrylic polymer of Example 2 wasprepared by solution polymerization techniques, dispersed in water andneutralized with amine to form an anionic (meth)acrylic polymer.

In Example 3, the (meth)acrylic polymer of Example 1 was neutralizedwith amine and combined with additional aqueous medium,lithium-containing particles and electrically conductive carbonparticles to form an electrodeposition bath.

In Example 4, the anionic (meth)acrylic polymer of Example 2 wascombined with additional aqueous medium, lithium-containing particlesand electrically conductive carbon particles to form anelectrodeposition bath.

The electrodeposition baths of Examples 3 and 4 were then used toelectrodeposit a coating on an aluminum foil that was to serve as acathode in a lithium ion battery. The electrocoated cathodes were rollcalendered and evaluated for 1/2 cell coin cell discharge capacities(mAh/g) at various discharge rates. The results are reported in Table Ibelow.

Example 1

In a 4-neck, 2-liter glass reactor equipped with a temperature probe,nitrogen inlet, and stainless steel stir blade, the following materialsare added: deionized (DI) water (460 g) and Rhodapex AB-20 (1 g). Thereactor is heated to 75° C. under a nitrogen blanket with stirring.Concurrently, the pre-emulsion monomer feed containing DI water (200 g),Rheasoap SR10 (4.3 g), Rhodapex AB-20 (2.2 g), Triton N101 (4.3 g),2-ethylhexylacrylate (147 g), butyl acrylate (18 g), 56 wt % solution ofN-butoxymethylacrylamide in butanol (26.8 g), and methacrylic acid (120g) is stirred for 30 minutes in a separate glass flask. Once the watersolution in the reactor reaches 75° C., 5% of the pro-emulsion feed isadded at once followed by stirring for 5 minutes. Next, a solution of DIwater (28 g) and ammonium persulfate (0.5 g) is added at once to thereactor followed by stirring for 15 minutes. Next, the remainder of thepre-emulsion monomer feed and the initiator feed containing DI water (32g) and ammonium persulfate (0.2 g) is added simultaneously in separateaddition funnels over 150 minutes. After the feeds are complete, themixture is stirred at 75° C. for 2 hours. After the 2-hour hold, thereaction is cooled to 30° C. and poured through a 10-micron filter baginto a suitable container. The resulting latex has a Tg −13° C., aweight average molecular weight (Mw) of 96400, pH=3, and particle sizeof 119 nm.

Example 2

In a 4-neck, 2-liter glass reactor equipped with a temperature probe,nitrogen inlet, and stainless steel stir blade, the solvent butylcellosolve (174 g) is added. The reactor is heated to 140° C. under anitrogen blanket with stirring. The monomer feed consisting of2-ethylhexylacrylate (162 g), butyl methacrylate (36 g), 56 wt %solution of N-butoxymethylacrylamide in butanol (32.1 g), methacrylicacid (144 g), and tertiary-dodecyl mercaptan (11.3 g) is mixed and addedinto an addition funnel. The initiator feed consisting of Trigonox F-C50(7.26 g) and butyl cellosolve (48 g) is mixed and added into a secondaddition funnel. Once the solvent in the reactor reaches 140° C., themonomer feed and initiator feed are added simultaneously in separateaddition funnels over 180 minutes. After the feeds are complete, theaddition funnel containing the monomer feed is rinsed with butylcellosolve (12 g) and the reaction is stirred for 1 hour at 140° C.Next, a chaser feed containing Trigonox F-C50 (3.63 g) and butylcellosolve (4.8 g) is added over 30 minutes. Then the initiator feedfunnel is rinsed with butyl cellosolve (6 g) and the reaction is stirredfor 90 minutes at 140° C. Next, the reaction mixture is cooled to 100°C. and DI water (20 g) warmed to 70° C. is added over 10 minutes andthen the mixture is allowed to stir for 15 minutes. The following stepis to cool the reaction mixture to 88° C. and begin addition ofdimethylethanolamine (164.4 g) warmed to 70° C. over 1 hour. Then thefeed is rinsed with butyl cellosolve (9 g) and the reaction is stirredfor 15 minutes. Once this is complete, the resin is cooled to <80° C.and poured out into a suitable container. The resulting anionic(meth)acrylic polymer has a Tg −13° C., a weight average molecularweight (Mw) of 5556, and pH=8.9.

Example 3

35 grams of the (meth)acrylic polymer prepared as in Example 1 was addeddropwise to a stirring solution of 4.2 grams of DMEA in 966.5 grams Dlwater. To prepare an electrodeposition bath, 86.5 grams of this anionic(meth)acrylic polymer was then diluted with 95 grams of DI water. Next,6 grams of conductive carbon, C-Nergy™ Super C65 (commercially availablefrom Timcal Ltd.), was added and then the mixture was sonicated for 25minutes. 12.5 grams of LiFePO₄ (LFP) (commercially available fromPhostech Lithium Inc.) was then added in 4 equivalent portions with eachaddition followed by 5 minutes of sonication. An additional 10 minutesof sonication was performed to ensure a uniform dispersion. Finally, 600grams of deionized water and 74 grams of butyl cellosolve solvent wereadded to the bath. To perform coating by electrodeposition, a carboncoated aluminum foil (commercially available from MTI) was wired as anelectrode and placed in the stirring 75° F. (24° C.) bath containing athermocouple and heating/cooling coil that also acted as a counterelectrode. The voltage was then turned on for 75 seconds at 75 voltswith the current set to 1.5 amps. The coated foil was then allowed todry at room temperature before heating to 150° C. for 20 minutes. Theelectrocoated cathode was then tested in a half-cell coin cell and thebattery performance results are found in Table I.

Example 4

250 grams of the anionic (meth)acrylic polymer prepared as in Example 2was added slowly to 300 grams of water while mixing aggressively with aCowles blade mixer. To prepare an electrodeposition bath, 4.1 grams ofthe anionic (meth)acrylic polymer was then diluted with 176.8 grams ofDI water. Next, 3.6 grams of conductive carbon, C-Nergy™ Super C65(commercially available from Timcal Ltd.), was added and then themixture was sonicated for 25 minutes. 15.5 grams of LiFePO₄(commercially available from Phostech Lithium Inc.) was then added in 4equivalent portions with each addition followed by 5 minutes ofsonication. An additional 10 minutes of sonication was performed toensure a uniform dispersion. Finally, 600 grams of deionized water and74 grams of butyl cellosolve solvent were added to the bath. To performcoating by electrodeposition, a carbon coated aluminum foil(commercially available from MTI) was wired as an electrode and placedin the stirring 75° F. (24° C.) bath containing a thermocouple andheating/cooling coil that also acted as a counter electrode. The voltagewas then turned on for 75 seconds at 100 volts with the current set to1.5 amps. The coated foil was then allowed to dry at room temperaturebefore heating to 150° C. for 20 minutes. The electrocoated cathode wasthen tested in a half-cell coin cell and the battery performance resultsare found in Table I.

TABLE I ½ cell coin cell discharge capacities (mAh/g) at various c-ratesBath % capacity composition pigment/ionic retention LFP/C65/Ionic(meth)acrylic Discharge C-rate after 25 (meth)acrylic polymer weight(hrs.⁻¹) cycles at Example Exp't polymer ratio Li/c 0.2 1.0 1.6 6.4c-rate of 1 3 15-AHO- 62.5/30/7.5 12.3 2.1 160 125 101 0 96.4 096-A-4 415-AHO- 77.5/18/4.5 21.2 4.3 123 84 54 0 93.8 087-A-4

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

Although various embodiments of the invention have been described interms of “comprising”, embodiments consisting essentially of orconsisting of are also within the scope of the present invention.

What is claimed is:
 1. A method of producing an electrode for a lithiumion battery comprising: immersing an electrically conductive substrateinto an electrodepositable composition, the substrate serving as theelectrode in an electrical circuit comprising the electrode and acounter-electrode immersed in the composition, a coating being appliedonto or over at least a portion of the substrate as electric current ispassed between the electrodes, the electrodepositable compositioncomprising: (a) an aqueous medium; (b) an ionic (meth)acrylic polymer;and (c) solid particles comprising: (i) lithium-containing particles,and (ii) electrically conductive particles; wherein the composition hasa weight ratio of the solid particles to the ionic (meth)acrylic polymerof at least 4:1.
 2. The method of claim 1, wherein the substrate is afoil comprising aluminum, iron, copper, manganese, nickel, a combinationthereof, and/or an alloy thereof.
 3. method of claim 1, wherein theionic (meth)acrylic polymer is anionic.
 4. The method of claim 1,wherein the ionic (meth)acrylic polymer is prepared by organic solutionpolymerization techniques.
 5. The method of claim 1, wherein the ionic(meth)acrylic polymer is prepared by emulsion polymerization techniques.6. The method of claim 1, wherein the (meth)acrylic polymer is preparedby polymerizing a mixture of (meth)acrylic monomers including a(meth)acrylic acid monomer and at least partially neutralizing the(meth)acrylic polymer with a base.
 7. The method of claim 6 in which the(meth)acrylic acid is present in the mixture in an amount of at least 30percent by weight based on total weight of the mixture of (meth)acrylicmonomers.
 8. The method of claim 6 in which the mixture of (meth)acrylicmonomers includes a monomer having a Tg of −20° C. or less.
 9. Themethod of claim 8, wherein the low Tg monomer is present in the mixturein amounts of at least 30 percent by weight based on total weight of(meth)acrylic monomer.
 10. The method of claim 8 in which the low Tgmonomer comprises 2-ethylhexyl acrylate and/or butyl acrylate.
 11. Themethod of claim 1, wherein the lithium-containing particles compriseLiCoO₂, LiNiO₂, LiFePO₄, LiCoPO₄, LiMnO₂, LiMn₂O₄, Li(NiMnCo)O₂, and/orLi(NiCoAl)O₂.
 12. The method of claim 1, wherein the lithium-containingparticles are present in an amount of at least 50 percent by weight,based on the total weight of the solids in the composition.
 13. Themethod of claim 1, wherein the electrically conductive particlescomprise electrically conductive carbon particles.
 14. The method ofclaim 13, wherein electrically conductive carbon particles comprisecarbon black.
 15. The method of claim 1, wherein the composition has aweight ratio of the lithium-containing particles to the electricallyconductive particles in the composition of at least 3:1.
 16. The methodof claim 1, wherein the composition has the weight ratio of the solidparticles to the ionic (meth)acrylic polymer of at least 8:1.
 17. Themethod of claim 1, wherein the composition has a total solids content of1 to 5 percent by weight, based on the total weight of the composition.18. An electrodepositable composition comprising (a) an aqueous medium;(b) an ionic (meth)acrylic polymer; and (c) solid particles comprising:(i) lithium-containing particles, and (ii) electrically conductiveparticles; wherein the composition has a weight ratio of the solidparticles to the ionic (meth)acrylic polymer of at least 4:1.
 19. Thecomposition of claim 18, wherein the weight ratio is at least 8:1. 20.The composition of claim 18, wherein the ionic (meth)acrylic polymer isanionic.
 21. The composition of claim 18, wherein the ionic(meth)acrylic polymer is prepared by organic solution polymerizationtechniques.
 22. The composition of claim 18, wherein the ionic(meth)acrylic polymer is prepared by emulsion polymerization techniques.23. The composition of claim 18, wherein the (meth)acrylic polymer isprepared by polymerizing a mixture of (meth)acrylic monomers including a(meth)acrylic acid monomer and at least partially neutralizing the(meth)acrylic polymer with a base.
 24. The composition of claim 23 inwhich the (meth)acrylic acid is present in the mixture in an amount ofat least 30 percent by weight based on total weight of the mixture of(meth)acrylic monomers.
 25. The composition of claim 23 in which themixture of (meth)acrylic monomers includes a monomer having a Tg of −20°C. or less.
 26. The composition of claim 25, wherein the low Tg monomeris present in the mixture in amounts of at least 30 percent by weightbased on total weight of (meth)acrylic monomer.
 27. The composition ofclaim 25 in which the low Tg monomer comprises 2-ethylhexyl acrylateand/or butyl acrylate.
 28. The composition of claim 18, wherein thelithium-containing particles comprise LiCoO₂, LiNiO₂, LiFePO₄, LiCoPO₄,LiMnO₂, LiMn₂O₄, Li(NiMnCo)O₂, and/or Li(NiCoAl)O₂.
 29. The compositionof claim 18, wherein the lithium-containing particles are present in anamount of at least 50 percent by weight, based on the total weight ofthe solid particles.
 30. The composition of claim 18, wherein theelectrically conductive particles comprise electrically conductivecarbon particles.
 31. The composition of claim 18, wherein thecomposition has a weight ratio of the lithium-containing particles tothe electrically conductive particles in the composition of at least3:1.
 32. The composition of claim 18, wherein the composition has atotal solids content of 1 to 5 percent by weight, based on the totalweight of the composition.